The stretch forming process, often used to produce formed automotive, aerospace, as well as other types of components, requires the coordinated movements of various members of the forming apparatus in order to produce parts that meet or exceed customer requirements. The stretch forming process, which can be used on multiple types of materials, can be summarized in the following steps. As can be seen in FIGS. 1A, 1B, 2A, and 2B a blank 2 (consisting of one or more components) is held by one or more grippers 4 at one or more locations. The grippers 4 are then moved in pre-determined directions to place the blank 2 under tension. While under tension, the blank 2 is then wrapped around a forming die 6 that can either be stationary (as depicted in 1A and 1B) or non-stationary (as depicted in FIGS. 2A and 2B). Additional tension, known as post-stretch, may be applied to set the blank 2 into its final shape.
A number of manufacturers produce a variety of stretch forming/bending machinery (i.e. forming equipment or bender). Each model of forming equipment will typically have different degrees of freedom when compared to other models. Degrees of freedom may include the wrap angle, tension, elevation, and twist of the grippers. Each set of gripper trajectories are unique to the specific component (end product) that is being manufactured.
After the forming die is designed and manufactured, the die is secured to the forming equipment. The blank is cut to a specified size and inserted into the grippers that are located near the ends of the forming die. The grippers use mechanical and/or hydraulic actuation to hold portions of the blank securely in place. The grippers must then follow unique paths, or trajectories, in order to form the blank using the contour of the forming die. Development of these trajectories, or “part teaching,” is tedious and time consuming when done at the forming machine control console. It generally involves manual manipulation of each degree of freedom at incremental bend angles along the length of a part. This manual manipulation is done by visual inspection of the interface between the blank and the forming die. Each degree of freedom is adjusted at each bend angle increment, until the blank “appears” to be adjacent to and in contact with the contour of the forming die. Once these variables are developed manually, they are stored in a computer file that can be inputted into a computer so that the forming equipment may mimic the stored gripper trajectories. This part teaching process can often take hours, days or even weeks of development time for each individual component being produced. Additionally, this labor intensive process disrupts the production routine.